There are several leak points. On our B411, 1999, the port light frames were leaking. The exterior frame is two aluminum extrusions coupled with a " rubber" seal - this had deteriorated. The replaceable rubber seal is also a possible leak source - especially if it has dirt and algae on it. The last area is actually the o-ring on the rotating latch. Yes, the silicone grease does help on the latter two areas. Someone recently posted the O-ring size - search for O-ring in this forum. They are available from Mcmaster.com.
The replacement seals I sourced from Defender.com
The o-rings I got from Mcmaster.com
I dug out the degraded rubber between the aluminum extrusions. Covered both sides with blue tape. Forced Dow 795 into groove with a very small screwdriver and then filled the joint with 795. Scraped the excess with a backward facing razor blade. Waited 30 minutes and removed the tape.
My result was no leaks